A housing of a blowout preventer has a vertical bore. Sealing elements are positioned in recesses on opposed sides of the bore. The sealing elements are movable between a retracted position within the recesses and a sealing position in which they close off the bore. Rams are used to move the sealing elements between the retracted position and the sealing position. The rams are housed in ram chambers extending out horizontally from the housing.
When the sealing elements are moved by the rams into the sealing position, the sealing elements contain well pressure originating from below the sealing elements. However, existing blowout preventers can not be pressurized from above, as the pressure would tend to separate the sealing elements. The ability to pressurize from above enables equipment installed above the blowout preventer to be tested before the blowout preventer is opened in order to ensure that the equipment is assembled correctly and will not leak wellbore fluids to atmosphere. This protects the health and safety of rig workers, as well as the environment.